Ecophysiology matters: linking inorganic carbon acquisition to ecological preference in four species of microalgae (Chlorophyceae).

The effect of CO supply is likely to play an important role in algal ecology. Since inorganic carbon (C ) acquisition strategies are very diverse among microalgae and C availability varies greatly within and among habitats, we hypothesized that C acquisition depends on the pH of their preferred natural environment (adaptation) and that the efficiency of C uptake is affected by CO availability (acclimation). To test this, four species of green algae originating from different habitats were studied. The pH-drift and C uptake kinetic experiments were used to characterize C acquisition strategies and their ability to acclimate to high and low CO conditions and high and low pH was evaluated. Results from pH drift experiments revealed that the acidophile and acidotolerant Chlamydomonas species were mainly restricted to CO , whereas the two neutrophiles were efficient bicarbonate users. CO compensation points in low CO -acclimated cultures ranged between 0.6 and 1.4 μM CO and acclimation to different culture pH and CO conditions suggested that CO concentrating mechanisms were present in most species. High CO acclimated cultures adapted rapidly to low CO condition during pH-drifts. C uptake kinetics at different pH values showed that the affinity for C was largely influenced by external pH, being highest under conditions where CO dominated the C pool. In conclusion, C acquisition was highly variable among four species of green algae and linked to growth pH preference, suggesting that there is a connection between C acquisition and ecological distribution.